The present invention is directed to a coating process used in manufacturing a mirror having improved quality and durability. The process of depositing thin layers of reflective metal such as silver and/or copper on transparent glass sheets to make mirrors is well known. The thin layer of metal, if not protected from the environment, will rapidly deteriorate. It is known to coat the metal side of the mirror with an opaque protective coating. However, while providing a good measure of protection on the metallic layer from corrosive elements in the environment, the metal layer often nevertheless corrodes, most often beginning at the edge of the mirror where it has been cut to a predetermined shape. Failure also can occur where the protective coating has been marred or abraded during shipping and handling of the mirror. Additionally, the protective coating on a mirror, often referred to as a "mirror back coating" or simply "mirror backing," should be able to harden or cure quickly to a sufficient degree to allow rapid manufacture of the coated mirror without the protective coating suffering from poor resistance to handling. The composition also should cure so as to provide good fabrication properties as required for edge grinding and for clean cutting and breaking.
A problem with conventional mirrors having thereon a conventional opaque, pigmented mirror back coating is that the mirror back coating tends not to have a desirable degree of abrasion resistance, stain resistance, chemical resistance and scratch resistance. However, applying an unpigmented clear coating over the opaque coating typically, while improving some of these properties with respect to the central portion of the coated surface, most often tends to induce failure at the edges of the mirror coating as evidenced by delamination of the entire coating from the edge of the mirror and thereby exposing the mirror to severe failure.
The present invention is directed to providing mirrors having a protective coating which provides excellent durability properties such as chemical resistance, solvent resistance, abrasion resistance as well as excellent fabrication and handling properties. Other objects of the invention will become apparent to the reader infra.